Making FLUSH TABLES WITH READ LOCK block COMMITs of existing transactions,

in a deadlock-free manner. This splits locking the global read lock in two steps.
This fixes a consequence of this bug, known as:
BUG#4953 'mysqldump --master-data may report incorrect binlog position if using InnoDB'
And a test.


sql/handler.cc:
  making COMMIT wait if FLUSH TABLES WITH READ LOCK happened.
sql/lock.cc:
  an additional stage so that FLUSH TABLES WITH READ LOCK blocks COMMIT:
  make_global_read_lock_block_commit():
  taking the global read lock is TWO steps (2nd step is optional; without
  it, COMMIT of existing transactions will be allowed):
  lock_global_read_lock() THEN make_global_read_lock_block_commit().
sql/mysql_priv.h:
  new argument to wait_if_global_read_lock()
sql/sql_class.h:
  THD::global_read_lock now an uint to reflect the 2 steps of global read lock (does not block COMMIT / does)
sql/sql_db.cc:
  update for new prototype
sql/sql_parse.cc:
  implementing the two steps of global read lock so that FLUSH TABLES WITH READ LOCK can block COMMIT without deadlocking with COMMITs.

3 files changed, 73 insertions, 0 deletions

diff --git a/mysql-test/r/flush_block_commit.result b/mysql-test/r/flush_block_commit.result
new file mode 100644
index 00000000000..3205dd9dad9
--- /dev/null
+++ b/mysql-test/r/flush_block_commit.result
@@ -0,0 +1,23 @@
+drop table if exists t1;
+create table t1 (a int) type=innodb;
+begin;
+insert into t1 values(1);
+flush tables with read lock;
+select * from t1;
+a
+ commit;
+select * from t1;
+a
+unlock tables;
+begin;
+select * from t1 for update;
+a
+1
+begin;
+ select * from t1 for update;
+ flush tables with read lock;
+commit;
+a
+1
+unlock tables;
+drop table t1;
diff --git a/mysql-test/t/flush_block_commit-master.opt b/mysql-test/t/flush_block_commit-master.opt
new file mode 100644
index 00000000000..d1f6d58e9f7
--- /dev/null
+++ b/mysql-test/t/flush_block_commit-master.opt
@@ -0,0 +1 @@
+--innodb_lock_wait_timeout=5
diff --git a/mysql-test/t/flush_block_commit.test b/mysql-test/t/flush_block_commit.test
new file mode 100644
index 00000000000..20ecec1361c
--- /dev/null
+++ b/mysql-test/t/flush_block_commit.test
@@ -0,0 +1,49 @@
+# Let's see if FLUSH TABLES WITH READ LOCK blocks COMMIT of existing
+# transactions.
+# We verify that we did not introduce a deadlock.
+
+-- source include/have_innodb.inc
+
+connect (con1,localhost,root,,);
+connect (con2,localhost,root,,);
+connect (con3,localhost,root,,);
+connection con1;
+drop table if exists t1;
+create table t1 (a int) type=innodb;
+
+# blocks COMMIT ?
+
+begin;
+insert into t1 values(1);
+connection con2;
+flush tables with read lock;
+select * from t1;
+connection con1;
+send commit; # blocked by con2
+sleep 1;
+connection con2;
+select * from t1; # verify con1 was blocked and data did not move
+unlock tables;
+connection con1;
+reap;
+
+# No deadlock ?
+
+connection con1;
+begin;
+select * from t1 for update;
+connection con2;
+begin;
+send select * from t1 for update; # blocked by con1
+sleep 1;
+connection con3;
+send flush tables with read lock; # blocked by con2
+connection con1;
+commit; # should not be blocked by con3
+connection con2;
+reap;
+connection con3;
+reap;
+unlock tables;
+connection con1;
+drop table t1;